The invention relates to a photo mask and, more particularly, to a method for repairing a bridge in a photo mask.
As semiconductor devices have become more highly integrated, the sizes of patterns formed on wafers have continuously decreased. To form such fine patterns, a photolithography process using a photo mask is typically used. Although there are various types of photo masks, a phase shift mask in particular functions to effectively lower the spatial frequency of a pattern by appropriately shifting the phase of light on the mask, or utilizes the effect of interference for increasing edge contrast. It is known that performing an exposure process using a phase shift mask is efficient to realize high resolution and to increase the depth of focus. During the fabrication of the phase shift mask, however, defective patterns may be generated, causing a bridge between neighboring phase shift layer patterns. The existence of the defective pattern may make it impossible to transcribe a desired pattern on a wafer, thereby causing device defects. Accordingly, it is necessary to remove the defective pattern causing a bridge, prior to processing a photolithography process.
FIGS. 1 to 3 are sectional views illustrating a conventional method for repairing a bridge in a photo mask. Referring to FIG. 1, a phase shift layer pattern 110 and a light shielding layer pattern 120 are disposed, from bottom to top, on a transparent quartz substrate 100. The phase shift layer pattern 110 is typically formed of a molybdenum silicon nitride (MoSiN) layer, and the light shielding layer pattern 120 is typically formed of a chromium (Cr) layer. As mentioned above, during the fabrication of the photo mask, a defective pattern 112 may be generated, causing a bridge between neighboring portions of the phase shift layer pattern 110.
Referring to FIG. 2, to remove the defective pattern 112, a laser beam 222 is irradiated onto the defective pattern 112. When occasion demands, an ion beam may be used, instead of the laser beam. In either case, a shielding layer 210 having an opening 211 is used to protect a normal pattern. The beam 222 is irradiated onto the defective pattern 112 through the opening 211 of the shielding layer 210, so as to remove the defective pattern 112. However, if the shielding layer 210 is incorrectly aligned, it may cause a beam 224, having passed through the shielding layer 210, to be irradiated onto the light shielding layer pattern 120 adjacent to the defective pattern 112. In this case, as shown in FIG. 3, damage may occur to a resulting pattern that should be essentially normal, as designated by reference numeral “310”, and damage may also occur to the transparent substrate 100 as designated by reference numeral “320.”